STUDY OF HYDROGEN DIFFUSION IN TITANIUM HYDRIDE USING NUCLEAR MAGNETIC-RESONANCE TECHNIQUES

In the γ-phase of TiHx, hydrogen atoms are known to occupy the tetrahedral interstitial sites which form a simple cubic sublattice in the FCC titanium host. To determine whether diffusing H atoms jump to nearest neighbor (NN) or third nearest neighbor (3 NN) sites, NMR measurements of (1), the diffusion coefficients of H between 450 °C and 550 °C and (2), the hydrogen spin system longitudinal relaxation time, T1 between 80 °C and 550 °C are presented for TiH1.55 and TiH1.71. From the relationship D=ƒTL2/(6τd), the jump length, L, is determined from the measured diffusion coefficients, D, and values of the mean residence time between atomic hops τd, normally calculated from T1 relaxation data. However, it is shown that existing T1 relaxation models in the literature lack sufficient accuracy to adequately determine τd from T1 data for the TiH1.55 and TiH1.71 hydrides. A computer simulation T1 relaxation model which includes spatial self, pair, and temporal correlation effects is developed. The model is applied to NN and 3 NN hopping on a simple cubic lattice. For each jump mechanism, values of T1-1 versus ɷτd are presented for several hydrogen concentrations. An analysis of the temperature dependence of T1 by this new model suggests that the activation energy for hydrogen motion in γ-TiHx, is approximately 9% higher than previously reported. For γ-TiHx, it is shown that hydrogen predominantly jumps to NN sites. © 1979, Akademische Verlagsgesellschaft, Wiesbaden